Double Chocolate Tangerine Mousse Cake

Cake:
1 cups unsalted butter
9 oz. Semi-sweet chocolate -- chopped
3/4 cup sugar
5 large eggs
1/2 cup ground toasted hazelnuts

Mousse:
3 cups strained fresh tangerine juice
1/3 cup sugar
2-1/2 tsp. Unflavored gelatin
3 tbsp. Fresh lemon juice
14 oz. Imported white chocolate -- chopped
6 tbsp. Sour cream
2 cups chilled whipping cream

Garnish:
9 oz. Imported white chocolate -- shaved into curls
Unsweetened cocoa powder
Fresh raspberries
Fresh mint sprigs

Cake:
Preheat oven to 325 degrees. Grease 9-inch springform pan with 2-1/2 inch sides. Line bottom with greased & floured parchment. Melt butter & chocolate in heavy saucepan over low heat, stirring constantly until smooth & melted. Remove from heat & whisk in sugar, eggs & ground nuts. Pour batter into prepared pan bake cake until toothpick inserted into center comes out with moist crumbs attached, about 45 minutes. Cool completely on rack -- cake will fall & crack. Release cake pan sides; brush sides of pan with vegetable oil. Set cake in center of pan. (There will be space around the cake that will be filled with the mousse.) Chill the cake.

Mousse:
Boil tangerine juice & sugar in heavy pot until reduced to 1-1/2 cups, about 20-25 minutes. Meanwhile, sprinkle gelatin over lemon juice in a small bowl & allow to soften. Add gelatin mixture to tangerine juice mixture & stir to dissolve add 14 ounces white chocolate & whisk over low heat until melted. Whisk in sour cream. Pour into large bowl. Chill just until cool & thickened, but not set, whisking occasionally, about one (1) hour, 45 minutes. Beat chilled whipping cream to stiff peaks. Fold into white chocolate mixture. Pour mousse over cake in pan, covering top & sides completely. Refrigerate cake overnight. Using vegetable peeler, shave 9 ounces white chocolate into thin curls. (if white chocolate is too hard to shave, place briefly in warm place to soften slightly.) Run small sharp knife around pan sides to loosen cake. Release pan sides. Place cake on platter. Sprinkle chocolate curls over top of cake. Press more chocolate curls over top of cake, covering completely. Place cocoa powder in fine sieve. Dust cocoa powder very lightly over chocolate curls. This cake can be prepared one day in advance. Cover & chill. When ready to serve, garnish with berries & mint.